The construction and utilization of electronic motor controls is well understood. For example, electronic motor controls have included variable frequency controllers and solid-state motor controllers (SoftStarts). For various reasons discussed below, none of the prior art electronic motor controls are suitable for use in applications where there is a hazardous/classified environment, and where there is a need for speed control or reduced voltage starting in a limited package space. For example, none of the prior art devices are suitable for the control of a motor in an oil refinery tank farm that requires speed control within a hazardous/classified environment. It is believed that other similar applications exist where there is a need for a limited package space motor speed control or reduced voltage starting that can operate within a hazardous/classified environment.
Electro-mechanical hazardous location motor starters are well known in the art. Typically an electric motor is started by an electromechanical motor starter. The electromechanical contactor closes a set of contacts to allow the motor to run. However, the ability to precisely control motor speed or reduced voltage motor starting is not available by this method. Across the line starting of motors has a higher current draw and on some larger motors may exceed the current limits set by the power utility.
Solid-state controllers (SoftStarts) and variable frequency controllers are able to closely control voltage applied to the motor, thus reducing the current used. However, electronic motor controls are known to produce large amounts of heat, which can be hazardous when used within a hazardous/classified environment. The means to dissipate the large amount of heat produced by these controllers has been an issue.
Large, purged enclosures have been utilized for this purpose, with the addition of purging equipment and at times air conditioning. This method has proved expensive as well as bulky which tends prevent use where space is limited. The Purge System format (even when applied per NFPA 496) has a potential for an explosion and loss of life. No system has been developed, prior to the current invention, to prevent the potential for catastrophic failure due to system failure. The Purge System also is not capable of containing an explosion. It was this safety issue that was a major driving factor for the current invention.
Another option has been to place the solid-state controller outside the hazardous/classified area. This option can also be a costly alternative since the increased distance from the solid state controller to the motor can require heavier cables and possibly a larger solid state controller.
Accordingly there exists a need for an electronic motor controller that is compact and suitable for use in hazardous/classified environments, such as for the control of a motor in an oil refinery tank farm.